/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.jsf.el;

import java.beans.FeatureDescriptor;
import java.util.Iterator;
import javax.el.ELContext;
import javax.el.ELException;
import javax.el.ELResolver;
import javax.faces.context.FacesContext;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.BeansException;
import org.springframework.lang.Nullable;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.jsf.FacesContextUtils;

/**
 * Special JSF {@code ELResolver} that exposes the Spring {@code WebApplicationContext}
 * instance under a variable named "webApplicationContext".
 *
 * <p>In contrast to {@link SpringBeanFacesELResolver}, this ELResolver variant
 * does <i>not</i> resolve JSF variable names as Spring bean names. It rather
 * exposes Spring's root WebApplicationContext <i>itself</i> under a special name,
 * and is able to resolve "webApplicationContext.mySpringManagedBusinessObject"
 * dereferences to Spring-defined beans in that application context.
 *
 * <p>Configure this resolver in your {@code faces-config.xml} file as follows:
 *
 * <pre class="code">
 * &lt;application>
 *   ...
 *   &lt;el-resolver>org.springframework.web.jsf.el.WebApplicationContextFacesELResolver&lt;/el-resolver>
 * &lt;/application></pre>
 *
 * @author Juergen Hoeller
 * @see SpringBeanFacesELResolver
 * @see org.springframework.web.jsf.FacesContextUtils#getWebApplicationContext
 * @since 2.5
 */
public class WebApplicationContextFacesELResolver extends ELResolver {

    /**
     * Name of the exposed WebApplicationContext variable: "webApplicationContext".
     */
    public static final String WEB_APPLICATION_CONTEXT_VARIABLE_NAME = "webApplicationContext";


    /**
     * Logger available to subclasses.
     */
    protected final Log logger = LogFactory.getLog(getClass());


    @Override
    @Nullable
    public Object getValue(ELContext elContext, @Nullable Object base, Object property) throws ELException {
        if (base != null) {
            if (base instanceof WebApplicationContext) {
                WebApplicationContext wac = (WebApplicationContext) base;
                String beanName = property.toString();
                if (logger.isTraceEnabled()) {
                    logger.trace("Attempting to resolve property '" + beanName + "' in root WebApplicationContext");
                }
                if (wac.containsBean(beanName)) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Successfully resolved property '" + beanName + "' in root WebApplicationContext");
                    }
                    elContext.setPropertyResolved(true);
                    try {
                        return wac.getBean(beanName);
                    } catch (BeansException ex) {
                        throw new ELException(ex);
                    }
                } else {
                    // Mimic standard JSF/JSP behavior when base is a Map by returning null.
                    return null;
                }
            }
        } else {
            if (WEB_APPLICATION_CONTEXT_VARIABLE_NAME.equals(property)) {
                elContext.setPropertyResolved(true);
                return getWebApplicationContext(elContext);
            }
        }

        return null;
    }

    @Override
    @Nullable
    public Class<?> getType(ELContext elContext, @Nullable Object base, Object property) throws ELException {
        if (base != null) {
            if (base instanceof WebApplicationContext) {
                WebApplicationContext wac = (WebApplicationContext) base;
                String beanName = property.toString();
                if (logger.isDebugEnabled()) {
                    logger.debug("Attempting to resolve property '" + beanName + "' in root WebApplicationContext");
                }
                if (wac.containsBean(beanName)) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Successfully resolved property '" + beanName + "' in root WebApplicationContext");
                    }
                    elContext.setPropertyResolved(true);
                    try {
                        return wac.getType(beanName);
                    } catch (BeansException ex) {
                        throw new ELException(ex);
                    }
                } else {
                    // Mimic standard JSF/JSP behavior when base is a Map by returning null.
                    return null;
                }
            }
        } else {
            if (WEB_APPLICATION_CONTEXT_VARIABLE_NAME.equals(property)) {
                elContext.setPropertyResolved(true);
                return WebApplicationContext.class;
            }
        }

        return null;
    }

    @Override
    public void setValue(ELContext elContext, Object base, Object property, Object value) throws ELException {
    }

    @Override
    public boolean isReadOnly(ELContext elContext, Object base, Object property) throws ELException {
        if (base instanceof WebApplicationContext) {
            elContext.setPropertyResolved(true);
            return true;
        }
        return false;
    }

    @Override
    @Nullable
    public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext elContext, Object base) {
        return null;
    }

    @Override
    public Class<?> getCommonPropertyType(ELContext elContext, Object base) {
        return Object.class;
    }


    /**
     * Retrieve the {@link WebApplicationContext} reference to expose.
     * <p>The default implementation delegates to {@link FacesContextUtils},
     * returning {@code null} if no {@code WebApplicationContext} found.
     *
     * @param elContext the current JSF ELContext
     * @return the Spring web application context
     * @see org.springframework.web.jsf.FacesContextUtils#getWebApplicationContext
     */
    @Nullable
    protected WebApplicationContext getWebApplicationContext(ELContext elContext) {
        FacesContext facesContext = FacesContext.getCurrentInstance();
        return FacesContextUtils.getRequiredWebApplicationContext(facesContext);
    }

}
